Welding gases are a common commodity in most industrial settings and even in home workshops, and they are used in various ways in the welding process. The most common types of welding gases shield the welding arc from contaminants such as air and dust. Their other function is as a fuel to heat metal.
Gases are one of two categories: inert or reactive. Inert gases will not change or create change when they contact other substances. Reactive gases generate a change of state in the additional material or themselves.
Inert gases allow the welding process to be accomplished without impurities weakening the weld. Reactive gases provide a positive change during welding, enhancing the way the material is joined.
Here are the gases used in welding, starting with the six shielding gases that are essential for high-quality arc welds:
The Effect of Shielding Gas on Welding
When the air gets into a welding arc, it causes air bubbles to form within the molten metal, producing a weak and unattractive weld. The shielding gas's primary purpose is to protect the weld pool from specific contaminants such as oxygen, nitrogen, and hydrogen. The reaction of these elements with the weld pool can create issues including porosity and spatter.
Most shielding gases are inert, making them ideal for shielding the welding process. They remain stable during the welding process and assist the weld in several ways, including increased fluidity, better penetration, a smoother bead surface, and the desired mechanical properties in the finished weld.
The Types of Welding Gases Used for Shielding
The first two shielding gases, argon, and helium, are inert, while the other four—hydrogen, oxygen, carbon dioxide, and nitrogen—are semi-inert.
· Argon (Ar): Used primarily when welding stainless steel and aluminum, argon also works on carbon steel with arc stability and continuous metal transfer from the weld pool's electrode. Argon is the top choice for TIG welding and excellent shielding gas for MIG.
· Helium (He): More expensive than other gases, helium provides deep penetration and increases the heat input. While it can be hard to get a consistent arc start with helium alone, it works well when blended with argon while counteracting its inconsistent starting properties.
· Carbon Dioxide (CO2): The most common shielding gas for MIG welding, CO2 costs less than argon but does not produce identical high-quality welds. However, when mixed with argon, there is less spatter and better-looking welds.
· Oxygen (O2): Oxygen is typically mixed with other shielding gases because it changes the fluidity of the molten metal. It can also speed up the welding process and minimize spatter.
· Nitrogen (N): Another inexpensive shielding gas, nitrogen increases weld penetration and arc stability when mixed with other gases. These blends can also enhance the chemical properties of alloys containing nitrogen.
· Hydrogen (H): When added to argon, hydrogen provides deeper penetration and faster welding speeds. The mixture of hydrogen, argon, and carbon dioxide can improve weld penetration. However, if misused, hydrogen may cause porosity.
Other Gases Used in Welding
The following three reactive gases are used in oxy-fuel welding and are highly flammable.
Acetylene: Relatively cheap and highly combustible, acetylene combines with oxygen as a fuel source in specific types of welding. By producing a hot flame, it can cut or weld most metals.
Propane: Not appropriate for gas welding, propane is used primarily for brazing after the welding process is completed. Propane is a flammable and combustible gas used in many applications as a fuel source.
Propylene: While not a pure gas (it's blended with oxygen), propylene burns at a substantially higher heat than propane and oxygen, making it suitable for non-structural fusion welding, brazing, and heating.